What are two major muscles used when flexing your arm?

1. Biceps brachii: The biceps brachii is a muscle located on the front of the upper arm. It is divided into two heads, the long head and the short head. The long head originates from the scapula, while the short head originates from the humerus. Both heads insert onto the radius, one of the two bones of the forearm. The biceps brachii is responsible for flexing the elbow joint.

2. Brachioradialis: The brachioradialis is a muscle located on the forearm. It originates from the humerus and inserts onto the radius. The brachioradialis is responsible for flexing the elbow joint and supinating the forearm, which is the movement of turning the palm up.